To reduce power consumption, some electronic systems power down various sub-systems at times that the sub-systems are not needed. Such systems monitor operational conditions to determine whether a particular sub-system is needed and should be powered up. For example, a communication sub-system may be powered down when no communications have been received for a predetermined time. While the communication sub-system is powered down, the system monitors a communication medium for indications of attempted communication and powers up the communication sub-system if an attempted communication is identified.